The present invention relates to a nail gun provided with an air duster which ejects compressed air for removing dust, wood chips and wood shavings out of an intended nail driving area.
Laid open Japanese Patent Application publication No.Hei 10-109280 discloses, as shown in FIGS. 1 and 2, a nail gun 601 having nail driving function A and duster function B. The nail gun 601 includes a main housing 602 and a handle 602A. In the main housing 602 a compressed air chamber 603 is provided, and a cylinder, a piston and a driver blade are disposed. The piston is reciprocally movable in the cylinder by pneumatic pressure applied in the compressed air chamber 603 through a hose 602B, and the driver blade extends from the piston for driving a head of a nail. A safety arm 611 is axially movably provided at a lower portion of the main housing 602. The safety arm 611 has a tip end abuttable on a workpiece. A magazine 620 is also provided at the lower portion of the main housing 602 for accommodating therein nails. A trigger lever 610 is provided near the handle 602A and cooperated with the safety arm 611 for driving the nail into the workpiece upon pulling the trigger lever 610 by the pneumatic pressure applied to the piston from the compressed air chamber 603 after depressing the safety lever 611 onto the workpiece.
An exhaust cover 621 is provided at an upper end of the main housing 602, and an duster nozzle 624 is provided in the exhaust cover 621. The duster nozzle 624 has a nozzle opening with a reduced diameter. A pressure release valve 622 is provided in the exhaust cover 621 for selectively communicating the compressed air chamber 603 with the duster nozzle 624 through first and second air passages 625 and 626. The pressure release valve 622 is connected to an operation button 623 positioned near the handle 602A, so that an operator can push the operation button 623 by a finger while gripping the handle 602A with remaining fingers of the same hand. For cleaning a surface of the workpiece before nail driving operation, the duster nozzle 624 is directed toward the surface is and the operation button 623 is depressed. As a result, a compressed air in the compressed air chamber 603 is ejected out of the duster nozzle 624 to remove the dust, wood chips and wood shavings.
FIG. 2 shows a detail of the pressure release valve 622. The compressed air chamber 603 is communicated with the pressure release valve 622 through the first air passage 625, and the pressure release valve 622 is communicated with the duster nozzle 624 through the second air passage 626. The pressure release valve 622 includes a valve stem 622A axially movable within a valve bush 629. An O-ring 627 is disposed over the valve stem 622A for constantly shutting off air communication between atmosphere and the second air passage 626. Another O-ring 628 is disposed over the valve stem 622A and is seatable on a valve seat section of the valve stem 622A for shutting off air communication between the first and second air passages 625 and 626 when the operation button 623 is not manipulated, and for communicating the first air passage 625 with the second air passage 626 when the operation button is depressed. The O-ring 628 and the valve bush 629 provide a first cylindrical sealing area with a diameter C, and the O-ring 627 and the valve bush 629 provide a second cylindrical sealing area with a diameter D which is smaller than the diameter C. The O-ring 628 defines a pressure release valve chamber 631 in which a compression spring 630 is interposed between an end wall of the valve chamber 631 and an inner end of the valve stem 622A. The valve stem 622A is biased toward the operation button 623 by the biasing force of the compression spring 630 and the pneumatic pressure in the compressed air chamber 603.
For driving the nail, the pneumatic pressure ranging from 0.98 to 2.45 Mpa is required, whereas for duster function the required pneumatic pressure is in a range of from 0.39 to 0.83 Mpa, which is lower than the nail driving pressure. Here, compressed air in the compressed air chamber 603 serves as a power source for driving the nail as well as for ejecting air through the duster nozzle 624. Therefore, the duster pressure must be the same as the nail driving pressure. Because the nail driving pressure cannot be lowered, the duster pressure is undesirably high. When the excessively high pressure is ejected from the nozzle 624, the air can raise up a cloud of dust around the user, or the nail gun 601 can move around uncontrollably due to reaction force, or loud ejection noise may be generated. If the inner diameter of the nozzle opening of the duster nozzle 624 is reduced in an attempt to reduce the pressure level of the ejected air, treble sound is generated at the nozzle opening, or the first O-ring 628 may be disengaged from an annular O-ring groove formed in the outer peripheral surface of the valve stem 622A due to application of high pressure to the first O-ring 628 from the is compressed air chamber 603.